Having Trouble With This Little Dog That Isn't Mine.

Name is Jessie not me, the dog. A little mutt...who is a cute little guy but I'm not buying him. He was left here by my wife's girl friend who is to depressed to take care of him. She a dog walker/care taker and she can't even take care of her own dog. I want my own dog but my wife doesn't want the do that one again. We use to have a great dog a German Shepherd " Tiga" Trained and everything. But she's adopted this one, without any indication of the true owner taking it back. The dog does not like me and barks and growls when I try to get into bed.
I am not digging this mutt. And I love dogs...but not this one...I feel a little guilty...because he so small. But he does nothing for me. God help me if he bites me....